Throughout its history, the golf ball has undergone an extensive evolution in an effort to improve its play-related characteristics, e.g., durability, distance, and control. Modern day golf balls can be classified as one-piece, two-piece, and three-piece (also known as “wound”) balls. One-piece balls are formed from a homogeneous mass of material with a dimple pattern molded therein. One-piece balls are inexpensive and very durable, but do not provide great distance because of relatively high spin and low velocity.
Two-piece balls are the most popular types of ball in use today. They are made by molding a cover around a solid core. Three-piece or wound balls are made by molding a cover about a wound core. The cores, which may include one or more core layers, whether wound or solid, typically measure from 1.4 to 1.6 inches (3.5 to 4.1 cm) in diameter. The cover, which may include one or more cover layers, is molded about the core to form a golf ball having the minimum United States Golf Association (USGA) specified diameter of 1.68 inches (4.3 cm). Typically, the cover has a thickness of about 0.04 inches (0.1 cm). Two-piece balls typically have a hard “cutproof” cover which gives a longer distance ball, but which has lower spin rates, resulting in a decreased ability to control the ball.
Conventionally, the process of molding the cover about the core for both two-piece and three-piece golf balls includes one of two procedures: injection molding of fluid cover stock material around the core, which is held in a retractable pin mold; or by compression molding preformed half-shells about the core. The half-shells may be formed by forcing a prep material through an extruder die to form a shaped prep, and placing the shaped prep into a mold to form the half-shells. This procedure may be duplicated with respect to the one or more core layers, as well as other components of the golf ball, such as one or more cover layers.
FIG. 1 details one method known in the art for forming components of a golf ball, such as half-shells or a core or cover layer, via a compression molding process. In step 1 of this method, preps, or pieces of a material, are extruded into cylindrical shapes. After extrusion, the material is cut into desired lengths of preps and then loaded, in step 2, into jigs. A jig allows large numbers of preps to be held in the position and orientation needed in order to be place properly in a mold. For instance, the jig may be configured so that the preps may be loaded into a mold only in a particular orientation, such as orienting a cylindrical prep so that its curved portion contacts the lower portion of the mold. When loaded, the preps are positioned so that they form an array or matrix corresponding to the cavities of a mold plate.
In step 3, to facilitate fast production of the golf balls, the jigs are employed to rapidly load the preps into golf ball component molds. For instance, the jigs may have a mechanism that holds or grips the preps during transport from one work area to another, but quickly releases the preps once the jig is positioned over a mold plate. Once the preps have been loaded into the mold, the mold is then assembled and loaded into a mold press (step 4).In step 5, the press closes the mold to form the half-shells of golf balls, which may then be compression molded about the interior components of the golf ball.
One drawback with the above process is that the cylindrical preps must be properly oriented when loaded by the jig into the mold or else a volume of air may be trapped between a prep and mold. If air is trapped in the mold, a void will be introduced into the prep when the mold is compressed. For example, as shown in FIG. 2, where a cylindrical prep 20 is formed and positioned in mold 22 within mold cavity 24 with one of its flat faces pointed downward, the outer edges of that face will be in contact with the surface of mold 22 within mold cavity 24. If the core outer edge maintains contact, the prep will “trap” air between the surface of the face and mold cavity 24. When the mold press is closed onto mold 22, trapped air may produce voids in the outer surface of cylindrical prep 20.
Therefore, the jig or other device must perform the additional step of orienting the prep before loading it into the mold. Referring again to the example of cylindrical-shaped preps, the preps must first be oriented by the jigs so that they will not trap air when loaded into the mold. FIG. 3 shows an orientation of a cylindrical-shaped prep 20 that helps avoid the trapping of air when the mold press closes.
One disadvantage of the process described above is that the step of loading the preps into the jig so that all of the preps are oriented properly is a time consuming, manual processs. On occasion, this manual process can result in improper loading of a prep, which can lead to the mold defects described above. In addition, the preps can lose their proper alignment for a number of other reasons. Once loaded, for example, the mold may be moved or jarred so that a prep may move before the mold is closed. Removal of the jig also may cause a prep to become misaligned.
It would therefore be desirable to extrude preps shaped such that they would not require orientation before they were loaded into the mold. For example, preps formed with a non-cylindrical shape, such as a square-shape, would not require placement into the mold in a specific orientation, since no orientation of this shape would trap air between it and the mold. However, the extrusion process inhibits control over the shape of prep formed. This is explained as follows: rubber or polybutadiene or similar materials used to form components of the golf ball undergo thermal expansion as they exit an extruder die. Thus, these materials continue to deform after extrusion, forming a shape different than the shape of the opening at the die outlet end (i.e. the end of the die that the material exits). For example, where the die has a square-shaped opening at its outlet end, a prep forced through this die will thermally expand after extrusion, becoming rounded in shape. Depending upon the extent of expansion, this prep may ultimately form a shape that still remains highly sensitive to trapping air in the mold unless it has a particular orientation.
Therefore, there is a need for a system and method of forming a golf ball that overcomes the disadvantages that exist in the art.
There is also a need for a system and method of forming a golf ball component that can form preps shaped such that they need not have only one orientation in a mold cavity during molding in order to prevent the trapping of air in the mold. There is also a need for a system and method of forming a golf ball component that is less likely to trap air in a mold cavity based on the orientation of the component in the mold.
There is also a need for a system and method of forming desired shapes of materials that is able to compensate for thermal expansion of the materials during the extrusion process.